Magnetoresistive element and the use thereof as storage element in a storage cell array

ABSTRACT

The magnetoresistive element has a first ferromagnetic element, a nonmagnetic layer element, and a second ferromagnetic layer element arranged in such a way that the nonmagnetic layer element is disposed between the first ferromagnetic layer element and the second ferromagnetic layer element. The first ferromagnetic layer element and the second ferromagnetic layer element are formed of substantially the same material, but they differ in their extent parallel to the interface to the nonmagnetic layer element in that they have different measurements in at least one dimension. The magnetoresistive element is suitable both as a sensor element and as a memory element in a memory cell configuration.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a 371 of International Application No.PCT/DE99/02387, filed Aug. 2, 1999, which designated the United States.

BACKGROUND OF THE INVENTION FIELD OF THE INVENTION

Magnetoresistive elements are increasingly used as sensor elements or asmemory elements for memory cell configurations, so-called MRAMs (see S.Mengel, “Technologieanalyse Magnetismus Band 2, XMR-Technologien”,published by VDI Technologiezentrum Physikalische Technologien, August1997). In the art, the term “magnetoresistive element” refers to astructure which comprises at least two ferromagnetic layers and anonmagnetic layer disposed in between these. Depending on the design ofthe layer structure, a distinction is made between GMR element, TMRelement, and CMR element.

The term “GMR element” is used in the art for layer structures whichcomprise at least two ferromagnetic layers and a nonmagnetic, conductivelayer disposed between these and which exhibit the so-called GMR (giantmagnetoresistance) effect. The GMR effect refers to the fact that theelectrical resistance of the GMR element depends on whether themagnetizations in the two ferromagnetic layers are oriented parallel orantiparallel. The GMR effect is large compared with the so-called AMR(anisotropic magnetoresistance) effect. The AMR effect refers to thefact that the resistance in magnetized conductors parallel andperpendicular to the direction of magnetization differs. The AMR effectis a bulk effect which occurs in ferromagnetic single layers.

The term “TMR element” is used in the art for tunnelingmagnetoresistance structures which comprise at least two ferromagneticlayers and an insulating, nonmagnetic layer disposed between these. Theinsulating layer is so thin as to give rise to a tunneling currentbetween the two ferromagnetic layers. These layer structures likewiseexhibit a magnetoresistive effect which is caused by a spin-polarizedtunneling current through the insulating, nonmagnetic layer disposedbetween the two ferromagnetic layers. In this case, too, the electricalresistance of the TMR element depends on whether the magnetizations inthe two ferromagnetic layers are oriented parallel or antiparallel. Therelative change in resistance here is from about 6 percent to about 30percent.

The term “CMR effect” describes a further magnetoresistive effect.Because of its measurement (relative change in resistance by from 100 to400 percent at room temperature) it is referred to as colossalmagnetoresistance (CMR) effect. It requires a high magnetic field,because of the high coercitivities it involves, to switch between themagnetization states.

U.S. Pat. No. 5,477,482 proposed an annular configuration of theferromagnetic layers and the nonmagnetic layer of a CMR element, therings being stacked on top of one another or being nestedconcentrically.

It has been proposed (see for example S. Tehrani et al., IEDM 96-193 andD. D. Tang et al., IEDM 95-997) to use GMR elements or TMR elements asmemory elements in a memory cell configuration. The memory elements areconnected in series via read lines. Running transversely to these areword lines which are insulated both with respect to the read lines andwith respect to the memory elements. Signals applied to the word linesgive rise to a magnetic field which is a consequence of the currentflowing within the word line and which, if sufficiently strong, affectsthe memory elements located underneath. The memory cell configurationexploits the fact that the resistance of the memory elements differs,depending on whether the magnetizations in the two ferromagnetic layersare oriented parallel or antiparallel to one another. To writeinformation, the direction of magnetization of the one ferromagneticlayer is therefore pinned, while that of the other ferromagnetic layeris switched. To this end, crossing lines, which are also referred to asxy lines and which cross at the memory cell to be written to, are fedwith signals in such a way that a magnetic field sufficient forremagnetization is produced at the crossing point.

Pinning the direction of magnetization in the one ferromagnetic layer isachieved by an adjacent antiferromagnetic layer which pins themagnetization (see D. D. Tang et al., IEDM 95-997) or by differing layerthicknesses of the ferromagnetic layers (see S. Tehrani et al., IEDM95-193). Here, the antiferromagnetic layer differs in materialcomposition from the adjacent ferromagnetic layer whose magnetizationstate is pinned.

As a result of the different layer thicknesses of the two ferromagneticlayers, a higher magnetic field is required in the one ferromagneticlayer to affect the direction of magnetization than in the other one. Towrite information, the magnetic field is assigned such a level that itis able to affect only the direction of magnetization in the one of thetwo ferromagnetic layers. The direction of magnetization in the otherferromagnetic layer, which can only be switched over by means of anincreased magnetic field, therefore remains unaffected thereby.

As the layer thickness of the ferromagnetic layer cannot, on the onehand, drop below a minimum layer thickness of about 5 nm owing tofabrication constraints, and on the other hand the maximum layerthickness of the ferroelectric layer in a GMR or TMR element is alsolimited—by the fact that a defined direction of magnetization parallelto the layer plane must be present—it is necessary in this case for theswitching magnetic field to be set precisely.

SUMMARY OF THE INVENTION

The object of the present invention is to provide a magnetoresistiveelement which overcomes the above-noted deficiencies and disadvantagesof the prior art devices and methods of this general kind, and which canbe fabricated in good yields within the context of semiconductor processtechnology and which is insensitive in terms of setting the switchingmagnetic field.

With the above and other objects in view there is provided, inaccordance with the invention, which can be used advantageously, interalia, as a memory element in a memory cell configuration or as a sensorelement.

In a first embodiment, the magnetoresistive element comprises thefollowing features:

a plurality of planar layer elements, including a first ferromagneticlayer element, a nonmagnetic layer element on the first ferromagneticlayer element and forming an interface therewith, and a secondferromagnetic layer element on the nonmagnetic layer element and formingan interface therewith, the planar layer elements defining a stack witha layer sequence;

the first ferromagnetic layer element and the second ferromagnetic layerelement comprising essentially the same material and having respectivemeasurements in a dimension perpendicular to the layer sequencediffering by at least percent relative to one another, and preferably by30%.

In other words, the magnetoresistive element comprises a firstferromagnetic layer element, a nonmagnetic layer element, and a secondferromagnetic layer element which are arranged in such a way that thenonmagnetic layer element is disposed between the first ferromagneticlayer element and the second ferromagnetic layer element. In thisarrangement, the nonmagnetic layer element has one interface each bothwith the first ferromagnetic layer element and with the secondferromagnetic layer element. The first ferromagnetic layer element andthe second ferromagnetic layer element comprise essentially the samematerial. The first ferromagnetic layer element and the secondferromagnetic layer element have different measurements in at least onedimension parallel to the interface with the nonmagnetic layer element.

As a result of this different shape of the first ferromagnetic layerelement and the second ferromagnetic layer element, the magnetic fieldsrequired to switch over the directions of magnetization in theferromagnetic layer elements differ. This effect is referred to as shapeanisotropy. Since in each layer element the measurements perpendicularto the layer thickness are distinctly larger than the layer thickness,larger differences in this measurement are possible in the presentmagnetoresistive element than is possible regarding the layer thicknessin the element proposed in S. Tehrani et al., IEDM 96-193. These largerdifferences in measurement result in distinctly different magnetic fieldstrengths required to switch over the direction of magnetization in therespective layer. Thus the magnetoresistive element is less sensitivewith respect to the precise setting of the switching magnetic field.

As the first ferromagnetic layer element and the second ferromagneticlayer element consist of essentially the same material, themagnetoresistive element can be fabricated using semiconductor processtechnology, especially silicon process technology with the thermal loadsof about 450° C. occurring there. In this temperature range, diffusionis to be expected, given the diffusion mobility of elements present inmagnetoresistive layer systems, especially Fe, Co, Ni, Cu etc., thediffusion modifying the characteristics of the ferromagnetic layerelements. The feared diffusion results in a change in the materialcomposition in the interface zones, which adversely affects thespin-dependent electron transport on which the magnetoresistive effectsin these elements are based. Even minor diffusion-caused migrations ofmaterial over a distance in the range from 1 to 5 nm beyond theseinterfaces are therefore expected to lead to considerable changes in themagnetic and electrical characteristics. The use of an antiferromagneticlayer to pin the direction of magnetization in one of the ferromagneticlayers therefore likewise appears to be problematic, since theantiferromagnetic layer must differ, in terms of material composition,from the ferromagnetic layer, and these diffusion processes between theadjacent layers are expected to result in a change in the materialcomposition.

This problem is overcome in the magnetoresistive element according tothe invention in that the two ferromagnetic layer elements consist ofessentially the same material, so that no concentration gradient arisesbetween the two ferromagnetic layer elements. The absence of aconcentration gradient between the two ferromagnetic layer elementscauses the driving force for a diffusion-caused material transportbeyond the nonmagnetic layer element to disappear.

Parallel to the interface with the nonmagnetic layer element, theferromagnetic layer elements can have any cross section.

In the first embodiment of the invention, the first ferromagnetic layerelement, the nonmagnetic layer element and the second ferromagneticlayer element are configured as planar layer elements which are joinedtogether to form a layer stack. In this case, the measurements of thefirst ferromagnetic layer element and of the second ferromagnetic layerelement differ in at least one dimension which is perpendicular to thedirection of the layer sequence. At the same time, it is within thescope of the invention for the first ferromagnetic layer and the secondferromagnetic layer to have essentially identical measurements in adimension perpendicular to the layer sequence.

In accordance with an added feature of the invention, the thicknesses ofthe ferromagnetic layer elements are between 2 nm and 20 nm.Perpendicular to the layer thickness, the measurement of the firstferromagnetic layer element is from 50 nm×80 nm to 250 nm×400 nm andthat of the second layer element from 65 nm×80 nm to 350 nm×400 nm, adifference of from at least 20 percent to 30 percent existing in onedimension. The cross section of the first ferromagnetic layer elementand of the second ferromagnetic layer element here is preferablyessentially rectangular. Alternatively, however, it can be round, ovalor polygonal.

There is also provided, in a further embodiment of the invention, amagnetoresistive element, comprising:

a plurality of layer elements having a hollow cylindrical shape with aprincipal cylinder axis, the layer elements including a firstferromagnetic layer element, a nonmagnetic layer element on the firstferromagnetic layer element and forming an interface therewith, and asecond ferromagnetic layer element on the nonmagnetic layer element andforming an interface therewith;

the first ferromagnetic layer element and the second ferromagnetic layerelement comprising substantially the same material; and

each of the layer elements having a respective inner diameter and arespective outer diameter, wherein one of the inner and outer diametersof the first ferromagnetic layer element differs from a respective inneror outer diameter of the second ferromagnetic layer element, and whereinthe first ferromagnetic layer element, the nonmagnetic layer element,and the second ferromagnetic layer element are stacked in a direction ofthe principal axes of the hollow cylinders.

In other words, the first ferromagnetic layer element, the nonmagneticlayer element, and the second ferromagnetic layer element are each ofannular shape, the ring widths of the first ferromagnetic layer elementand of the second ferromagnetic layer element differing from oneanother. The first ferromagnetic layer element, the nonmagnetic layerelement and the second ferromagnetic layer element have the shape of ahollow cylinder and are stacked in the direction of the principal axesof the hollow cylinders. The shape anisotropy of the magnetic switchingfield is implemented in this embodiment by the differing ring widths,i.e. half the difference of outer diameter and inner diameter of eachhollow cylinder, of the first ferromagnetic layer element and of thesecond ferromagnetic layer element. The thicknesses of the firstferromagnetic layer element and of the second ferromagnetic layerelement are each from 2 nm to 20 nm. The outer diameter of the firstferromagnetic layer element and of the second ferromagnetic layerelement are in the range of between 50 nm and 400 nm, the outerdiameters and/or inner diameters of the first ferromagnetic layerelement and the second ferromagnetic layer element differing by from 20percent to 50 percent. In one embodiment, the outer diameter of thefirst ferromagnetic layer element is from 75 nm to 300 nm and the outerdiameter of the second ferromagnetic layer element is from 100 nm to 400nm.

In accordance with an additional feature of the invention,

the first ferromagnetic layer element and the second ferromagnetic layerelement each has a thickness of between 2 nm and 20 nm and the outerdiameters of the first ferromagnetic layer element and the secondferromagnetic layer element are in a range from 50 to 400 nm; and

at least one of the outer diameters and the inner diameters of the firstferromagnetic layer element and the second ferromagnetic layer elementdiffer from 20 percent to 50 percent.

In accordance with another feature of the invention,

the outer diameter of the first ferromagnetic layer element is from 75nm to 300 nm and a thickness of the first ferromagnetic layer elementparallel to the principal axis is from 2 nm to 20 nm; and

the outer diameter of the second ferromagnetic layer element is from 100nm to 400 nm and a thickness of the second ferromagnetic layer elementparallel to the principal axis of the cylinder is from 2 nm to 20 nm.

With the above and other objects in view there is also provided, in yeta further embodiment of the invention, a magnetoresistive element,comprising:

a plurality of layer elements each having a hollow cylindrical shape andbeing disposed concentrically with one another along a principalcylinder axis, the layer elements including a first ferromagnetic layerelement, a nonmagnetic layer element on the first ferromagnetic layerelement and forming an interface therewith, and a second ferromagneticlayer element on the nonmagnetic layer element and forming an interfacetherewith;

the first ferromagnetic layer element and the second ferromagnetic layerelement comprising substantially the same material;

the nonmagnetic layer element being disposed, in a radial direction withrespect to the hollow cylindrical shapes, between the firstferromagnetic layer element and the second ferromagnetic layer element;and

the first ferromagnetic layer element having a height in a directionparallel to the principal axis of the cylindrical shapes different froma height of the second ferromagnetic layer element.

In this third embodiment of the invention, the first ferromagnetic layerelement, the nonmagnetic layer element and the second ferromagneticlayer element are each in the form of a hollow cylinder and are arrangedconcentrically relative to one another, the nonmagnetic layer elementbeing disposed between the first ferromagnetic layer element and thesecond ferromagnetic layer element. The first ferromagnetic layerelement and the second ferromagnetic layer element in this case differin terms of their height parallel to the cylinder axis.

The height of the first ferromagnetic layer element is preferablybetween 50 nm and 250 nm, the height of the second ferromagnetic layerelement is between 80 nm and 400 nm, the difference in height beingbetween 30 nm and 150 nm and usefully being at least from 20 to 30percent. In another embodiment, the first ferromagnetic layer elementhas an outer diameter of between 70 nm and 400 nm, an inner diameter ofbetween 60 nm and 390 nm and a height, parallel to the principal axis ofthe cylinder, of between 35 nm and 180 nm, and the second ferromagneticlayer element ha s an outer diameter of between 60 nm and 390 nm, aninner diameter of between 50 nm and 380 nm and a height, parallel to theprincipal axis of the cylinder, of between 50 nm and 400 nm.

Preferably, the ferromagnetic layer elements each comprise at least oneof the elements Fe, Ni, Co, Cr, Mn, Gd, Dy. The nonmagnetic layerelement can be either conductive or nonconductive. Preferably, thenonmagnetic layer element provided is nonconductive and includes atleast one of the materials Al₂O₃, NiO, HfO₂, TiO₂, NbO and/or SiO₂ andhas a measurement, perpendicular to the interface with the ferromagneticlayer elements, in the range of between 1 and 4 nm. In this case, themagnetoresistive element is a TMR element which, compared with a GMRelement, has a high electrical resistance perpendicular to the tunnelinglayer.

Alternatively, the nonmagnetic layer element can be implemented in aconductive material, e.g. Cu, Au or Ag, and have a measurement,perpendicular to the interface with the ferromagnetic layer elements, offrom 2 nm to 4 nm.

Other features which are considered as characteristic for the inventionare set forth in the appended claims.

Although the invention is illustrated and described herein as embodiedin a magnetoresistive element and use thereof as a memory element in amemory cell configuration, it is nevertheless not intended to be limitedto the details shown, since various modifications and structural changesmay be made therein without departing from the spirit of the inventionand within the scope and range of equivalents of the claims.

The construction and method of operation of the invention, however,together with additional objects and advantages thereof will be bestunderstood from the following description of specific embodiments whenread in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1a is a top plan view onto a magnetoresistive element comprisingplanar layer elements, in which the measurements of a firstferromagnetic element and of a second ferromagnetic elementperpendicular to the directions of magnetization differ from oneanother;

FIG. 1b is a section taken along the line I—I in FIG. 1a;

FIG. 2a is a top plan view onto a magnetoresistive element comprisingplanar layer elements, in which the measurements of a firstferromagnetic layer element and of a second ferromagnetic layer elementparallel to the directions of magnetization differ from one another;

FIG. 2b is a section taking along the line II—II in FIG. 2a;

FIG. 3a is a top plan view onto a magnetoresistive element whichcomprises hollow-cylindrical layer elements which are stacked on top ofone another and differ in terms of their outer diameters;

FIG. 3b is a section taking along the line III—III in FIG. 3a;

FIG. 4a is a top plan view onto a magnetoresistive element whichcomprises hollow-cylindrical layer elements which are disposedconcentrically relative to one another and which differ in terms oftheir heights;

FIG. 4b is a section taking along the line IV—IV in FIG. 4a; and

FIG. 5 is a diagram of a detail of a memory cell configuration whichcomprises magnetoresistive elements as memory elements.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the figures of the drawing in detail and first,particularly, to FIGS. 1a and 1 b thereof, there is seen a firstferromagnetic layer element 11, a nonmagnetic layer element 13, and asecond ferromagnetic layer element 12. The elements are arranged on topof one another as a stack. The first ferromagnetic layer element 11 isof essentially rectangular shape with measurements of 130 nm×250 nm. Inthe direction of the layer sequence (vertical in FIG. 1b), the firstferromagnetic layer element 11 has a thickness of 10 nm. The nonmagneticlayer element 13 likewise has an essentially rectangular cross sectionwith measurements of 130 nm×250 nm. In the direction of the layersequence it has a thickness of 2 nm. The second ferromagnetic layerelement 12 has an essentially rectangular cross section withmeasurements of 200 nm×250 nm. In the direction of the layer sequence ithas a thickness of 10 nm.

The first ferromagnetic layer element 11 and the nonmagnetic layerelement 13 have the same length as the second ferromagnetic layerelement 12, but a smaller width than the second ferromagnetic layerelement 12. The first ferromagnetic layer element 11 and the nonmagneticlayer element 13 are centered, with respect to their width, on thesecond ferromagnetic layer element 12. Both in the first ferromagneticlayer element 11 and in the second ferromagnetic layer element 12 thereexist preferred directions of magnetization parallel to the length ofthe respective layer element 11, 12. The directions of magnetization areshown as double-headed arrows in FIG. 1a.

The first ferromagnetic layer element 11 and the second ferromagneticlayer element 12 have the same material composition. They consist of Co.The nonmagnetic layer element 13 consists of Al₂O₃.

The first ferromagnetic layer element 11 has a higher switchingthreshold than the second ferromagnetic layer element.

Referring now to FIGS. 2a and 2 bin this second exemplary embodiment,the first ferromagnetic layer element 21 made of Co, a nonmagnetic layerelement 23 made of Al₂O₃, and a second ferromagnetic layer element 22made of Co are arranged on top of one another. The first ferromagneticlayer element 21 is of essentially rectangular shape with a length of250 nm, a width of 130 nm and a thickness, in the direction of the layersequence, of 10 nm. The second ferromagnetic layer element 22 likewisehas an essentially rectangular cross section with a length of 200 nm, awidth of 130 nm and a thickness, in the direction of the layer sequence,of 10 nm. The nonmagnetic layer element has the same cross section asthe second ferromagnetic layer element 22 and has a thickness, parallelto the layer sequence, i.e., the stack direction, of 2 nm.

In the first ferromagnetic layer element 21 and in the secondferromagnetic layer element 22, magnetization states with directions ofmagnetization parallel to the length of the respective layer element 21,22 are adopted. The directions of magnetization are shown as adouble-headed arrow in FIG. 2a.

The second ferromagnetic layer element 22 and the nonmagnetic layerelement 23 are centered, in the length direction, on the firstferromagnetic layer element 21. In this arrangement, the firstferromagnetic layer element has a higher switching threshold than thesecond ferromagnetic layer element 22.

Referring now to FIGS. 3a and 3 b, in this third exemplary embodimentthe magnetoresistive element comprises a first ferromagnetic layerelement 31 made of NiFe, a second ferromagnetic layer element 32 made ofNiFe, and a nonmagnetic layer element 33 made of Al₂O₃. Each of theseelements has a cylindrical footprint. The first ferromagnetic layerelement 31, the nonmagnetic layer element 33 and the secondferromagnetic layer element 32 are arranged, in the direction of theprincipal axes of the hollow cylinders, to form a stack in which thenonmagnetic layer element 33 is disposed between the first ferromagneticlayer 31 and the second ferromagnetic layer element 32 and in which theaxes of the cylinders coincide, i.e., the individual elements arestacked coaxially.

The first ferromagnetic layer element 31 and the second ferromagneticlayer element 32 each have a thickness, parallel to the principal axis,of 10 nm. In the first ferromagnetic layer element 31 and the secondferromagnetic layer element 32, annular magnetization states establishthemselves which can be of clockwise or counterclockwise orientation.

The nonmagnetic layer element 33 has a thickness, parallel to theprincipal axis, of 2 nm. The outer diameter of the first ferromagneticlayer element 31 is 200 nm, the outer diameter of the secondferromagnetic layer element 32 is 250 nm, the inner diameters of all thelayer elements are 130 nm.

In this configuration, the first ferromagnetic layer element 31 has alarger switching threshold than the second ferromagnetic layer element32.

Analogously, the hollow-cylindrical layer elements stacked on top of oneanother can differ in terms of their inner diameters or inner and outerdiameters.

Referring now to FIGS. 4a and 4 b, in this fourth exemplary embodiment,a first ferromagnetic layer element 41 made of NiFe, a nonmagnetic layerelement 43 made of Al₂O₃, and a second ferromagnetic layer element 42made of NiFe are provided. Each of the elements has the shape of ahollow cylinder and they are disposed concentrically, i.e., coaxially,relative to one another. In this arrangement, the nonmagnetic layerelement 43 is disposed between the first ferromagnetic layer element 41and the second ferromagnetic layer element 42.

The first ferromagnetic layer element 41 has an outer diameter of about270 nm, an inner diameter of about 260 nm and an a height, parallel tothe principal axis of the hollow cylinder, of 180 nm. The nonmagneticlayer element 43 has an outer diameter of about 260 nm, a thickness of 2nm and a height, parallel to the principal axis of the hollow cylinder,of at least 180 nm. The second ferromagnetic layer element 42 has anouter diameter of about 258 nm, an inner diameter of about 250 nm and aheight, parallel to the principal axis of the hollow cylinder, of 250nm. The first ferromagnetic layer element 41 and the nonmagnetic layerelement 43 are centered, in terms of height, on the second ferromagneticlayer element 42.

In the first ferromagnetic layer element 41 and the second ferromagneticlayer element 42, magnetization is annular and can be oriented eitherclockwise or counterclockwise. The direction of magnetization in eachcase is shown as a double-headed arrow in FIG. 4a.

In this arrangement, the first ferromagnetic layer element 41 has ahigher switching threshold than the second ferromagnetic layer element42.

Referring now to FIG. 5, there is shown a memory cell configurationwhich comprises memory cells S, formed as magnetoresistive elements inaccordance with FIGS. 1a to 4 b: the memory elements S are arranged inthe form of a grid, each memory element S being connected between afirst line L1 and a second line L2. The first lines L1 run parallel toone another and cross the second lines L2 which likewise run parallel toone another. To write to a memory element S, such a current is appliedto the associated line L1 and the associated second line L2 that themagnetic field produced at the point where the first line L1 and thesecond line L2 cross one another and where the memory element S islocated is sufficiently large to switch the direction of magnetizationof the second ferromagnetic layer element. Here, the magnetic fieldeffective at the respective crossing point is a superposition of themagnetic field induced by the current flowing in the first line L1 andof the magnetic field induced by the current flowing in the second lineL2.

I claim:
 1. A magnetoresistive element, comprising: a plurality ofplanar layer elements, including a first ferromagnetic layer element, anonmagnetic layer element on said first ferromagnetic layer element andforming an interface therewith, and a second ferromagnetic layer elementon said nonmagnetic layer element and forming an interface therewith,said planar layer elements defining a stack with a layer sequence; saidfirst ferromagnetic layer element and said second ferromagnetic layerelement comprising essentially the same material and having respectivemeasurements in a dimension perpendicular to said layer sequencediffering by at least percent relative to one another, and said firstferromagnetic layer element and said second ferromagnetic layer elementfurther comprising at least one element selected from the groupconsisting of Cr, Mn, Cd, Dy; and said nonmagnetic layer elementcomprising at least one material selected from the group consisting ofNiO, HfO₂, TiO₂, NbO, SiO₂ and having a thickness in a range between 1nm and 4 nm.
 2. The magnetoresistive element according to claim 1,wherein the measurements of said first ferromagnetic layer element andsaid second ferromagnetic layer element in the dimension perpendicularto said layer sequence differ by at least 30 percent.
 3. Themagnetoresistive element according to claim 1, wherein said firstferromagnetic layer element has measurements perpendicular to said layersequence from 50 nm×80 nm to 250 nm×400 nm and a thickness parallel tosaid layer sequence between 2 nm and 20 nm; and said secondferromagnetic layer element has measurements perpendicular to said layersequence from 65 nm×80 nm to 350 nm×400 nm and a thickness parallel tosaid layer sequence between 2 nm and 20 nm.
 4. A magnetoresistiveelement, comprising: a plurality of layer elements having a hollowcylindrical shape with a principal cylinder axis, said layer elementsincluding a first ferromagnetic layer element, a nonmagnetic layerelement on said first ferromagnetic layer element and forming aninterface therewith, and a second ferromagnetic layer element on saidnonmagnetic layer element and forming an interface therewith; said firstferromagnetic layer element and said second ferromagnetic layer elementcomprising substantially the same material; and each of said layerelements having a respective inner diameter and a respective outerdiameter, wherein one of said inner and outer diameters of said firstferromagnetic layer element differs from a respective inner or outerdiameter of said second ferromagnetic layer element, and wherein saidfirst ferromagnetic layer element, said nonmagnetic layer element, andsaid second ferromagnetic layer element are stacked in a direction ofthe principal axes of said hollow cylinders.
 5. The magnetoresistiveelement according to claim 4, wherein said first ferromagnetic layerelement and said second ferromagnetic layer element each has a thicknessof between 2 nm and 20 nm and said outer diameters of said firstferromagnetic layer element and said second ferromagnetic layer elementare in a range from 50 to 400 nm; and at least one of said outerdiameters and said inner diameters of said first ferromagnetic layerelement and said second ferromagnetic layer element differ from 20percent to 50 percent.
 6. The magnetoresistive layer element accordingto claim 4, wherein said outer diameter of said first ferromagneticlayer element is from 75 nm to 300 nm and a thickness of said firstferromagnetic layer element parallel to the principal axis is from 2 nmto 20 nm; and said outer diameter of said second ferromagnetic layerelement is from 100 nm to 400 nm and a thickness of said secondferromagnetic layer element parallel to the principal axis of thecylinder is from 2 nm to 20 nm.
 7. The magnetoresistive elementaccording to claim 4, wherein said nonmagnetic layer comprises at leastone material selected from the group consisting of NiO, HfO₂, TiO₂, NbO,SiO₂ and has a thickness in a range between 1 nm and 4 nm.
 8. Themagnetoresistive element according to claim 4, wherein said firstferromagnetic layer element and said second ferromagnetic layer elementcomprise at least one element selected from the group consisting of Cr,Mn, Gd, Dy.
 9. A magnetoresistive element, comprising: a plurality oflayer elements each having a hollow cylindrical shape and being disposedconcentrically with one another along a principal cylinder axis, saidlayer elements including a first ferromagnetic layer element, anonmagnetic layer element on said first ferromagnetic layer element andforming an interface therewith, and a second ferromagnetic layer elementon said nonmagnetic layer element and forming an interface therewith;said first ferromagnetic layer element and said second ferromagneticlayer element comprising substantially the same material; saidnonmagnetic layer element being disposed, in a radial direction withrespect to said hollow cylindrical shapes, between said firstferromagnetic layer element and said second ferromagnetic layer element;and said first ferromagnetic layer element having a height in adirection parallel to said principal axis of said cylindrical shapesdifferent from a height of said second ferromagnetic layer element. 10.The magnetoresistive element according to claim 9, wherein the height ofsaid first ferromagnetic layer element is between 50 nm and 250 nm; theheight of said second ferromagnetic layer element is between 80 nm and400 nm; and a difference in the heights is between 30 nm and 150 nm. 11.The magnetoresistive element according to claim 9, wherein said firstferromagnetic layer element has an outer diameter of between 70 nm and400 nm, an inner diameter of between 60 nm and 390 nm and a height,parallel to the principal axis of the cylinder, of between 35 nm and 180nm; said second ferromagnetic layer element has an outer diameter ofbetween 60 nm and 390 nm, an inner diameter of between 50 nm and 380 nmand a height, parallel to the principal axis of the cylinder, of between50 nm and 400 nm.
 12. The magnetoresistive element according to claim 9,wherein said nonmagnetic layer comprises at least one material selectedfrom the group consisting of NiO, HfO₂, TiO₂, NbO, SiO₂ and has athickness in a range between 1 nm and 4 nm.
 13. The magnetoresistiveelement according to claim 9, wherein said first ferromagnetic layerelement and said second ferromagnetic layer element comprise at leastone element selected from the group consisting of Cr, Mn, Gd, Dy.